Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$29.73	7.251%	$31.8857	$31.89	$31.90	$31.90
Purchase #2	$52.82	4.204%	$55.0406	$55.04	$55.05	$55.00
Purchase #3	$121.45	7.768%	$130.8842	$130.88	$130.90	$130.90
Purchase #4	$97.96	13.676%	$111.357	$111.36	$111.35	$111.40
Purchase #5	$116.99	13.319%	$132.5719	$132.57	$132.55	$132.60
Purchase #6	$46.53	12.869%	$52.5179	$52.52	$52.50	$52.50
Purchase #7	$19.98	10.757%	$22.1292	$22.13	$22.15	$22.10
7 purchase totals =	$485.46		$536.3865	$536.39	$536.40	$536.40